A polarizing film used for an image display particularly for a liquid crystal display device) is required to have both of high transmittance and a high polarization degree in order to provide bright images of high reproducibility. The polarizing film has heretofore been produced by dyeing a film such as a polyvinylalcohol film with dichroic iodine or a dichroic substance such as a dichroic dye and then orienting the film by uniaxial stretching.
In recent years, due to an increase in demand for the liquid crystal display device, a demand for the polarizing film which is used for the liquid crystal display device has been increased. Further, a polarizing film having higher optical characteristics and excellent in in-plane uniformity free from irregularity, contaminant, and the like is in demand (see, for example, Reference 1). In order to increase an amount of production of the polarizing film with the high optical characteristics being maintained, increase in the number of polarizing films by means of expansion of current production equipment and a use of a film having a larger width have been tried. However, with such measures, time and a cost are incurred for the production equipment expansion, and it is difficult to manufacture the large width film, and it has been detected that the conventional method causes deterioration in optical characteristics and increases in irregularity and defect. Therefore, there is a demand for a method of conveniently increasing the production amount without deteriorating the optical characteristics. Though a method of stacking films and then stretching the stack film has been disclosed (see, for example, Reference 2) as such method, the method is specialized for the stretching part, and it is difficult to apply the method as it is to a series of production steps using a processing bath.
[Reference 1] JP-A-2001-290027
[Reference 2] WP-A-2002-333520
An object of this invention is to provide a convenient method for producing a polarizing film without deteriorating optical characteristics such as transmittance and a polarization degree, wherein the polarizing film is produced by using at least one processing bath. Another object of this invention is to provide the polarizing film obtainable by the production method, an optical film obtainable by stacking an optical layer on the polarizing film, and an image display using the polarizing film or the optical film.